Several years ago the American Gas Association began funding work intended to develop an improved method for laying gas pipelines on ocean bottoms. The existing method involved adding sections of pipe to an end of the pipeline that was supported on a barge floating on the ocean surface. The pipe sections comprised a metal core pipe covered with cement to make the pipe heavier than water, and the completed portion of the pipeline slanted from the barge down to the ocean bottom, with the trailing portion resting on the ocean bottom.
This method worked acceptably for laying pipelines at depths up to 500 feet. But at the greater depths contemplated in pursuit of added gas supplies, the increased length and weight of pipe from barge to ocean bottom could buckle or bend the pipe. Also, the increased weight of pipe would be a major obstacle in the event that defects or a storm required recovering the pipe.
The funding by the Gas Association led to a suggestion that the cement layer covering the pipe sections be filled with porous hollow spheres coated with a water-soluble coating. The coated hollow spheres would initially reduce the weight of the pipe; but after the pipe had been submerged for a week or so, water permeating into the cement would dissolve the coating on the spheres and fill the spheres, thereby weighing down the pipe to make it rest stably on the ocean bottom.
This approach apparently proved to be unworkable because it was not possible to accurately control the exposure of the water-soluble coating to water. Such exposure occurred when the coated spheres were mixed into wet cement, and also during storage, when rain and moisture in the air permeated into the cement. The exposure caused premature dissolving of the coating, causing variable and unpredictable performance by the pipe. In the end the approach of water-soluble-coated spheres was abandoned, leaving no practical method for laying pipeline at greater ocean depths.